As electronic technology advances, larger numbers of electronic components may be formed and interconnected as integrated circuitry on common substrates. Separate wire interconnections are still required, however, to connect integrated circuit chips to non-integrated circuit components and to other integrated circuits as well as connector leads and pins. These interconnections are typically accomplished by bonding one end of a selected interconnect wire to a first circuit point with the aid of a bonding tool. Thereafter, the length of the interconnect wire is then paid out to form a loop between the first circuit point and a selected second circuit point. The wire is then bonded to the second circuit point and the standing part of the wire is broken adjacent to the second circuit point.
Historically, this bonding has been accomplished by placing the end of a bonding tool against the upper surface of the wire and applying pressure to hold the lower surface of the wire against the circuit point to which the wire is to be bonded. Sonic energy is imparted to the wire and the circuit point at the end of the bonding tool to cause mechanical and electrical bonding of the wire and circuit point.
Regardless of the bonding technique utilized, those skilled in the art will recognize that the reliability of the related microelectronic systems is directly related to the tensile strength of the interconnect wires referenced above and the reliability of the bonds created at the first and second circuit points. Various methods and apparatus have thus been designed and used to determine the tensile strength of interconnect wires for research purposes as well as quality control measures during conventional production processes.
See, for example, U.S. Pat. No. 3,564,911 issued to J. W. Slemmons et al. which discloses a wire bond strength tester comprising a self-centering and self-damping hook which is suspended from one end of a balanced beam disposed for pivoting about a pivot point between the extremities. The beam is loaded with a weight as a function of a required pulling force to be applied by the hook assembly. In operation, a test circuit is moved under the hook and the beam is tilted to permit the hook to engage an interconnect wire of a microelectronic circuit. In operation, a wire is engaged and the beam is thereafter permitted to pivot upwards in response to the applied load. An upper mechanical stop is also provided to prevent excessive pivoting and to test the vertical slack of the conductor. If the bond of the interconnect wire or its vertical slack is within the required limits, the upper mechanical stop is not contacted and a successful test is indicated. In contrast, if a mechanical stop is contacted, an unsuccessful test is indicated.
U.S. Pat. No. 4,282,759 issued to Merrell discloses a method and apparatus for non-destructive testing of beam-lead integrated circuit connections. As disclosed by Merrell, a beam-leaded device is provided in which each individual lead has pull tab with a weakened area thereon in order to provide a non-destructive means for testing the beam leads. The beam-lead device is tested by inserting a hook of a gram pull tester into an opening at the tab and pulling on the tab until the weakened area is broken. The weakened area is selected such that it will break when subjected to a predetermined pull. This predetermined amount is selected to be less than that required to break the tensile strength of the diffusion bond between the beam-leads and the conductors to which they are connected.
U.S. Pat. No. 4,697,461 issued to Jabs discloses a method and apparatus for verifying the seismic integrity of an electronic component. According to the invention, a force of a desired magnitude is applied to the lead of an electronic component contained in an electric circuit. The magnitude of the force corresponds to the expected maximum force which would be exerted on the lead by an earthquake. An indication is thus provided when the lead has been subjected to the applied force for a given period of time corresponding to the approximate period of time the maximum force of an earthquake would be exerted on the lead. This force is released if the desired magnitude has been applied for a further preset period of time which is greater than the given period of time, or if the magnitude of the applied force exceeds a preset maximum value.
U.S. Pat. No. 4,453,414 issued to Ronemus et al. discloses a method of testing the bond strength between a lead and an electrical device which includes mounting the device to a pedestal which is coupled to a load sensor. As disclosed by Ronemus, the lead is pulled from the device by a freely manipulatable grasping tool. A load differential indicated by the load sensor is observed as an indication of the bond strength between the lead and the device. The apparatus in accordance with the invention includes a support arm which is movable along a predetermined path and to which is mounted a pedestal for supporting a device, the leads of which are to be pull tested. A predetermined bias force resists a movement of the arms such that a movement of the arm registers a predetermined minimal pull strength of the leads.
U.S. Pat. No. 4,907,458 issued Biggs et al. discloses a method and apparatus for testing microcircuitry bonds. According to the invention, a wire bond is engaged by a hook, and the force with which that wire is urged to move away from the hook is measured as the force required to maintain the hook stationary. In the preferred method, the hook is fixed to a structure whose vertical position remains substantially fixed while the magnitude of the pulling force is measured. The vertical position of the electronic apparatus remains fixed while the hook is moved vertically and rotationally to place the hook under a wire notwithstanding that such a method requires capability of vertical movement of both the electronic apparatus and the hook.
U.S. Pat. No. 4,895,028 issued to Mayer discloses a method of pull-testing wire connectors on an electrical device. According to the invention, an upward pulling force is applied to a wire loop by a motor-driven loading arm through a hook which is connected to the free end of a flexible cantilever beam in the arm. A strain gauge is provided in the beam to measure its deflection and thus the applied pulling force and supply a signal corresponding to this measured force. The actual force is applied to the bonds and is calculated by generating a signal signifying the distance the hook has moved when the strain gauge starts to generate a signal.
The conventional prior art devices discussed above provide a general background in respect of the design and use of pull testing methods and apparatus for determining bond and tensile strength. For the most part, these device have been used in connection with conventional manufacturing processes to ensure the reliability of the selected bonds and interconnect wires.
While the prior art systems provide a broad indication of tensile strength, they do not provide any indication of the specific failure mode, i.e. whether there has been a break at the center span, upper bond, lower bond, or a lift of the respective bonds. From a research standpoint, this information is of critical importance to provide meaningful feedback for the selection of future interconnect wires having varying diameters, length and bonds. At present, technicians must visually inspect such failure modes and record the resultant information on an individual basis. As readily seen, this approach requires substantial labor and resultant costs which inevitably must be passed on to the consumer.